Arrangement for limit switches



Nov. 20, 1962 J. M. YOSENICK ARRANGEMENT FOR LIMIT SWITCHES 2 Sheets-Sheet l Filed Dec. 25, 1960 L3] L27 L/7 INVENTOR. John M. Yosen/ck Z X Nov. 20, 1962 J. M. YOSENICK 3,065,315

ARRANGEMENT FOR LIMIT SWITCHES Filed Dec. 23. 1960 2 Sheets-Sheet 2 KWwMV K John M. Yosenick United btates 3,065,315 ARRANGEMENT FOR LlMlT SWITHES John M. Yoseniclr, Carpentersville, llL, assignor to Automatic Electric Laboratories, Inc., Northlake, Iil., a corporation of Delaware Filed Dec. 23, 196i), Ser. No. 77,972 6 Claims. (Cl. zoo-47) This invention relates to switching devices, and more particularly to limit switches such as those commonly used on various machines in controlling, for example, the movement of a particular element of the machine. It is directed particularly to controlling the punching operations of a conventional punch press.

In such a control system, the limit switch serves as a sentinel to give indication of faulty operation of a machine. The limit switch, for example, may be actuated by a pilot pin associated in a well known manner with the punch of a punch press and serves to protect the elements of the machine by switching electrical power from the clutch or from the drive motor.

The main object of my invention is the provision of a simple and economical limit switch to facilitate opera tion of a machine, such as a punch press, in controlling the operation of a moving element on a machine, for example, a punch.

A further object of my invention is to provide a lowvoltage electrical system for such a limit switch, which frees the operator of hazards from electrical shocks.

A feature of this invention is the provision of a limit switch which is easily adjustable in small increments relative to its mounting. This adjustment can be made very quickly and economically by unskilled labor.

Another feature is an adjusting arrangement within the limit switch allowing the limit switch to be actuated at any predetermined point along the path of travel of the machine element being controlled.

Briefly, the embodiment of the machine described herein comprises a limit switch having a mounting, a movable contact operated by a plunger, and a stationary contact. The switch is adjustable in the mounting so that the outer end of the plunger can be moved into contact, preferably both physically and electrically, with the machine element which is to be controlled. A light, a relay, and a low-voltage source are used in combination with the limit switch. The light provides a means of adjusting the limit switch and it also serves as a warning signal to the operator which indicates faulty punch press operation, while the relay controls the power circuit of the clutch of the press for stopping movement of the punch.

The invention will be more fully understood from the following detailed description of an embodiment thereof. In the accompanying drawings:

FIG. 1 is a perspective view of the switch in the normal position but adjusted so that its plunger contacts the movable member of the machine to be supervised; a cutaway shows the size and shape of the contact elements in the housing of the limit switch.

FIG. 2 is a cross-section of the limit switch in the above position along line 2-2 of FIG. 1.

FIG. 3 is a cross-section of the limit switch along line line 2-2 after slight actuation of the plunger and just prior to separation of the contacts.

FIG. 4 is a cross-section of the limit switch along line 22 with the plunger in the same position as in FIG. 3, but with the tension adjusting screw loosened somewhat.

FIG. 5 shows one arrangement of the circuit which may be used in conjunction with the limit switch.

Referring now to the drawings, FIGS. 1 and 2 show the limit switch in its normal position but already adice justed to engage the movable member of the machine. A mounting 1 is bolted to machine 12 and has housing 2 of the limit switch, which is of electrical insulating material, threaded therein. The limit switch has an actuating plunger 3 resiliently held in its outermost position by a relatively strong spring 9. Mounting 1 is secured to machine 12 by screws 16 and 17. Housing 2 may be Y threaded into the housing 2. Sleeve it carries at its left end, as viewed in FIGS. 1 and 2, a jack portion 13 into which a banana plug or the like, not shown, may be inserted for providing the necessary electrical connection, shown in detail in FIG. 5, for the circuit elements controlled by the limit switch. The jack portion 13 of sleeve 5 is, on its outside, covered with insulating material 15. A screw it surrounded by a sleeve 7 of electrical insulating material along most of its exposed length, is threaded into the inner end of actuating plunger 3. A washer-shaped movable contact element 6 rides on the insulating sleeve 7, and is normally held against stationary contact element 4 by a relatively weak spring 8 which is normally somewhat compressed by a corresponding adjustment of screw it as described in detail hereafter.

According to one feature of the invention, limit switch 14 has two contacts which are eifectively connected in series. One contact, designated as I in FIGS. 1 to 5, is a normally closed contact and comprises contact elements 4 and 6 referred to above. The other contact, designated as II in the drawings, is a normally open contact and it comprises the outer end of metallic plunger 3 as one contact element, and as the other element, thelikewise metallicmovable member ll of the machine, the frame of which is connected to ground. Thus, with the limit switch adjusted so that plunger 3 just touches movable member 11, a circuit path extends from movable member ll by way of plunger 3, the shaft and head of screw 10, spring 8, movable contact element 6, stationary contact element 4, and the body portion and jack portion of sleeve 5 to the banana plug (not shown).

In FIG. 3, machine element 11 has been actuated slightly and the plunger 3 has thereby been moved from its position shown in FIGS. 1 and 2 to a point where the inner end of the plunger is about to touch the movable contact element 6 and separate it from contact element 4-. It is noted that spring 8 has steadily expanded and has continued to hold movable contact 6 against contact 4 during the aforementioned movement of plunger 3. This lost-motion of the inner end of plunger 3 prevents separation of the contacts 4 and 6 from the shock and vibration imparted to the die during normal punching operations.

FIG. 4 shows the plunger 3 in the same position as shown in FIG. 3, but in the initial adjustment of the limit switch the screw it has been screwed out of plunger 3 somewhat. It can be seen that adjustment of the sep aration point of contact elements 4 and 6 may be accomplished by means of the initial setting of screw 10. If screw it is backed out of the plunger 3 a short distance, the tension on spring 3 is reduced. Then, as actuating plunger 3 is urged into the housing by movable member 11, spring 8 expands to its normal uncompressed length so that upon further movement of plunger 3, to-

gether with screw 10, to the left as viewed in FIG. 4, contact element 6 separates from contact element 4 before the inner end of plunger 3 reaches contact 6. Thus it is observed, by adjusting screw contacts 4 and 6 can be adjusted to separate at any point along the path of travel of the plunger 3. This separation may be brought about simply by washer 6 riding on insulating sleeve 7 and being frictionally taken along by it under this condition. If the limit switch is mounted on the machine with the outer end of plunger 3 pointing vertically up, washer 6 would separate from washer 4 due to gravity. Alternatively, the ends of spring 8 may be fastened such as by welding, to the head of screw 10 and to washer 6, respectively.

The pilot pin, or other movable member 11, is conventionally made of hardened steel or similar material, thus it is capable of withstanding the wear and shock presented by the sheet material as it enters the press. The spring 8, within the limit switch, also serves to absorb some shock, since it does not allow contacts 4 and 6 to separate until the plunger has been moved more than a predetermined amount. Adjustment of the tension of spring 8 by screw it will vary the shock absorption capacity of switch 14.

In FIG. 5, a preferred version of the limit switch circuit containing a relay R1, a low-voltage source, and preferably also a portable signal light S1, is shown as it may be applied to conventional punch press control circuitry. The 3-phase line voltage is brought in at L1, L2, and L3, and all three line conductors are connected to the drive motor B through make contacts 521, 522, and 523 of relay R2. Relay R2 is unoperated until the start button C is depressed.

L1 and L2 continue to transformer A which has a 110 volt secondary. Tap wires from the 110 volt secondary go to transformer I where the voltage is stepped down to 8 volts. The 8 volt secondary of transformer I is the voltage source for the limit switch circuit proper. Limit switch contact II is shown in the open position but when the switch is properly adjusted, by means of the micrometer adjustment provided by the threads in housing 2 and mounting 1, and the press is running, the following circuit is established: from the 8 volt source, through relay R1, in parallel with portable signal light S1 when provided, contacts I and II to the frame ground of the machine. Relay R1 of this limit switch circuit is thus operated. Relay R1 at its contact 511 controls the circuit of signal light at which may be mounted at the top of the machine or some other convenient location. At its contact 512 relay R1 controls relay R3. Contact 531 of relay R3 controls clutch F which is interposed between motor E and the ram, not shown, which holds the punch. At G, H, K, and M there are shown miscellaneous controls which may include hand or foot operated switches, emergency stop switches, or other conventional control apparatus.

To observe the protective function of the limit switch, consider it to have been properly adjusted, so that contacts I and II are closed and relay R1 is operated. Lamp S1 lights to show the operator that the switch is in adjustment; in addition, lamp S2 on the top of the machine is lighted by contact 511 of relay R1 permitting supervisory inspection of the machine status. Contact 512 of relay R1 operates relay R3. Contact 531 of relay R3 operates the clutch P which begins reciprocation of the ram. At contact 432 a locking circuit is completed for relay R3. The machine is now operating, and parts are being punched from stock entering the press.

If, for example, the limit switch was being used on this particular occasion to check for misfeeding or double heading, the switch would have been positioned in contact with a pilot pin which in the normal operation of the machine, enters a prepunched hole in the stock each time the ram comes down. If, during any cycle, the stock is not feeding properly and the prepunched hole therefore does not come to the proper point, the pilot pin cannot enter the hole and it moves the limit switch plunger to the left, as viewed in FIGS. 1 to 4, which in turn breaks contact I, interrupting the series circuit. Relay R1, in releasing its contact 511 extinguishes signal light S2, and at its contact 512 releases relay R3 which in turn opens the operating and locking circuits of clutch F, thereby stopping the ram.

From the above description it will be noted that, if at the outset, the switch plunger is not properly adjusted by the operator to touch the pilot pin, no ground is obtained therefrom, relay R1 will remain unoperated and the press cannot operate. Also, if the operator, for example, by inadvertance, moves the limit switch out of its adjusted position during the operation of the machine contrary to the safety rules governing the operation of machines of this kind-then relay R1 in releasing will cause light S2 to be extinguished, thus indicating this unstandard condition to supervisory personnel.

It will also be appreciated that the micrometer adjustment of screw 10 of limit switch 14 and the provision of the additional contact II and the inclusion of the limit switch in a low-voltage circuit-which permits the use of simple contact elements such as 4 and 6 and 3 and 11, eliminates shock hazards and contribute individually and in coaction, to the economy, safety, and effectiveness of the limit switch arrangement according to the invention.

While the invention has been described with reference to a particular environment, other applications will be readily apparent to those skilled in the art. The invention, therefore, should not be limited to the particular arrangements shown and described but should cover all modifications within the spirit and scope of the claims.

What is claimed is:

1. A limit switch, for use on a machine which has a stationary member and a relatively movable member, threaded means being provided on said stationary member for mounting said switch thereon, said limit switch comprising: a contact, a housing comprising two portions, defining, when assembled, a. chamber enclosing said contact, a plunger slidably supported in said housing for actuating said contact, one end of said plun er extending outwardly of said housing for engagement by said movable member, said housing having a thread engaging the threaded means on said stationary member, so that said housing, as an assembled unit and with said switch therein, may be longitudinally adjusted in minute increments relative to said stationary member to effect correspond ing adjustment of the outer end of said plunger.

2. A supervisory arrangement for a machine which has a stationary member and a relatively movable member, said arrangement comprising a limit switch, threaded means for mounting said switch on said stationary member, said limit switch including: a first, normally closed, contact, a housing for said contact, a plunger slidably supported in said housing for actuating said first contact, one end of said plunger extending outwardly of said housing for engagement by said movable member, a second, normally open, contact controlled by the outer end of said plunger on the one hand and said movable memher on the other hand, said housing having a thread engaging the thread in said mounting means, so that said housing may be longitudinally adjusted in minute increments relative to said stationary member until said second contact closes, thereby establishing a circuit including said two contacts in series.

3. A supervisory arrangement as claimed in claim 2 wherein one contact element of said second contact is formed by said movable member and the other contact element by the outer end of said plunger, so that said second contact is closed upon physical abutment of said plunger end with said movable member; and wherein said circuit also comprises a low voltage source and supervisory means both for governing the operation of said machine and for giving a visual indication, under the control of said series-connected contacts.

4. A limit switch for use on a machine which has a stationary member and a relatively movable member, means for mounting said switch on said stationary member, said limit switch comprising: a housing adjustahly engaged in said mounting means, said housing having an actuating plunger siidably supported therein, one end of said plunger extending outwardly of said housing for engagement with said movable member, a contact in said housing including a stationary contact element and a movable contact element, said movable contact element controlled by said plunger, a first resilient means normally holding said plunger in its outermost position, a second resilient means normally holding said movable contact element against said stationary contact element, the inner end of said plunger being spaced from said movable contact element when said plunger is in the normal position, such that said plunger may be actuated through a certain predetermined distance before said movable contact element is separated from said stationary contact element.

5. A limit switch, for use on a machine which has a stationary member and a relatively movable member, means for mounting said switch on said stationary memher, said limit switch comprising: a housing, having a passage therein, adjustably engaging in said mounting means, one section of said passage having a relatively small bore, the other section having a relatively large bore, a stationary contact secured in the large bore of said housing, an actuating plunger slidably supported in said small bore, a movable contact controlled by said plunger, one end of said plunger extending outwardly of said housing for engagement with said movable memher, a first resilient means normally holding said plunger in its outermost position, a second resilient means normally holding said movable contact against said stationary contact, an adjusting means for said second resilient means, the inner end of said plunger being spaced from said movable contact when said plunger is in the normal position, such that the point along the path of the plunger at which said movable contact separates from said stationary contact as said plunger is actuated by said movable member is adjustable by adjusting the adjusting means of said second resilient means.

6. A limit switch, for use on a machine which has a stationary member and a relatively movable member, means for mounting said switch on said stationary member, said limit switch comprising: a housing of electrical insulating material having a passage therein, said housing adjustably engaged in said mounting means, one section of said passage having a relatively small bore, the other section having a relatively large bore, a stationary contact secured in said large here, an actuating plunger slidably supported in said small bore, a movable contact controlled by said plunger, one end of said plunger extending outwardly of said housing and normally in contact with said movable member, a first resilient means normally holding said plunger in its outermost position, a second resilient means normally holding said movable contact against said stationary contact, an adjusting means for said second resilient means, an electrical insulating means covering most of the longitudinal area of said adjusting means, a sleeve member engaged in said large bore and in contact with said stationary contact, said adjusting means adjustably engaging the inner end of said actu ating plunger, said sleeve member, stationary contact, movable contact, second resilient means, adjusting means, and actuating plunger forming an electrical conducting path, while said plunger is in the unactuated position.

References Cited in the file of this patent UNITED STATES PATENTS 1,468,985 Whittington Sept. 25, 1923 1,935,442 Goff Nov. 14, 1933 2,750,477 Brown et a1 June 12, 1956 2,845,608 Short July 29, 1958 2,899,511 Fraser Aug. 11, 1959 

